The invention relates to scintillation materials for use in radiation detectors operating under adverse temperature conditions.
Radiation detectors based on scintillation detectors are used, for example, in logging petroleum and geothermal deposits by .gamma.-ray detection or in monitoring nuclear power installations. These detectors, and the scintillation materials they use, must operate in adverse chemical and temperature environments, such as the brine-saturated, super-heated steam contaminated with volatile sulfur compounds found in association with geothermal deposits. The typical operating environment for such a scintillation material is from about 25 degrees Celsius to about 200 degrees Celsius or more.
Scintillation materials used in the past lose their efficiency as temperature increases. For example, thallium-activated sodium iodide loses efficiency at the rate of minus 0.2% per degree Celsius temperature rise and bismuth orthogermanate (Bi.sub.4 Ge.sub.3 O.sub.12) loses 2% per degree Celsius. At room temperature bismuth orthogermanate has a light output of only 8% of the output of thallium-activated sodium iodide and at 125 degrees Celsius its light output is 20% of the output that it has at room temperature.